For example, a pressurized water reactor (PWR: Pressurized Water Reactor), using light water as a reactor coolant and a neutron moderator, runs it as non-boiling, high-temperature and high-pressure water throughout a reactor core, sends the high-temperature and high-pressure water to a steam generator for generation of steam by heat exchange, and sends the steam to a turbine generator for generation of electricity. The pressurized water reactor transfers the heat of high-temperature and high-pressure primary cooling water to secondary cooling water by way of the steam generator, generating the steam from the secondary cooling water. In the steam generator, the primary cooling water flows inside a large number of narrow heat-transfer tubes, and the heat of the primary cooling water is transferred to the secondary cooling water flowing outside the heat-transfer tubes, thereby generating the steam, which causes the turbine to rotate for generating electricity.
In the steam generator, a tube bank external cylinder is arranged inside the sealed hollow barrel with a predetermined space from the inner wall thereof, a plurality of heat-transfer tubes of an inverted U shape are arranged inside the tube bank external cylinder, with each heat-transfer tube having its end supported by a tube plate and its middle part supported by a plurality of tube supporting plates that are supported by stay-rods extending from the tube plate, and a steam-water separator and a humidity separator are arranged in the upper part.
Therefore, when the primary cooling water is supplied to the plurality of heat-transfer tubes through a water chamber provided at the lower part of the barrel, and the secondary cooling water is supplied into the barrel from a water supply pipe provided at the upper part of the barrel, the heat exchange is performed between the primary cooling water (hot water) flowing inside the plurality of heat-transfer tubes and the secondary cooling water (cold water) circulating inside the barrel, so that the secondary cooling water absorbs the heat and the steam is generated. When the steam goes upward, the water is separated from the steam, and the steam is discharged from the upper end of the barrel while the water falls downward.
A conventional steam-water separator consists of a plurality of risers through which the steam goes upward, a swirl vane provided inside the riser, a downcomer barrel located outside the riser to form a downcomer space, and a deck plate having an orifice and a vent that is arranged opposite the upper end of the riser and the downcomer barrel with a predetermined space therefrom.
Therefore, two-phase flow of the steam and the water generated by the steam generator is introduced into each riser at its lower end, moving upward, and is lifted upward while whirling by the swirl vane, and the water deposits on the inner wall face of the riser and moves upward while becoming a liquid film flow and the steam moves upward while whirling at the upper part of the riser. The steam is delivered above the deck plate mainly through the orifice and the vent, and the water escapes out of the riser through an opening between the upper end of the riser and the deck plate, flowing into the downcomer barrel and then flows downward. Accordingly, only the steam flows out above the deck plate.
This type of steam-water separator is described in the Patent Documents 1 and 2 below.
In the conventional steam-water separator, most of the water flowing out of the riser from the upper end thereof into the downcomer barrel flows down through the downcomer barrel. However, some of the water escapes out of the downcomer barrel from the top thereof, and comes to flow out of the vent above the deck plate, being accompanied by the steam moving upwards outside the downcomer barrel, which decreases steam-water separating efficiency.
Therefore, in a steam-water separator as described in Patent Document 3 below, a swirl vane that swirls and lifts a mixture of water and steam is provided in the riser, and slits are formed below an upper opening of the riser and above the swirl vane. Thus, while being swirled and lifted in the riser by the swirl vane, the mixture is separated into a second mixture whose primary element is the water and a third mixture whose primary element is the steam. When the second mixture is lifted up to the height of the slits while being swirled, the second mixture is discharged through the slits into the downcomer barrel.
Patent Document 1: Japanese Patent Application Laid-Open No. S49-064972
Patent Document 2: Japanese Patent Application Laid-Open No. H05-346483
Patent Document 3: Japanese Patent Application Laid-Open No. 2001-079323